Influence of microstructure on micromagnetic Barkhausen emissions in AISI 4140 steel

The effects of microstructure on the micromagnetic Barkhausen signal emissions in AISI 4140 steel are reported. The Barkhausen signal amplitude is known to be highly sensitive to the type and distribution of microstructural inhomogeneities, such as grain boundaries, precipitates and dislocations. The Barkhausen measurements were taken on samples having pearlitic, spheroidized and bainitic microstructures. The Barkhausen emissions were measured in terms of rms voltage peak-to-peak voltage and number of events per cycle. It is shown that Barkhausen signals can be used to distinguish between pearlitic and bainitic microstructures.